Color-reactable inorganic adsorbent pigment and coating composition containing the same



United States Patent 3,223,546 COLOR-REACTABLE INORGANIC ADSORBENT PIGMENT AND COATING COMPOSITION CONTAINING THE SAME Glen A. Hemstock, East Brunswick, N.J., assignor to Minerals & Chemicals Philipp Corporation, Menlo Park, N.J., a corporation of Maryland No Drawing. Filed Jan. 17, 1962, Ser. No. 166,913 6 Claims. (Cl. 106288) This invention generally rel-ates to pressure-sensitive record material of the type utilizing multiple colorless, color-reactant materials which produce a colored mark upon adsorptive contact with eachother, as exemplified by the manifold record material described in US. 2,730,456 to Barrett K. Green and Lowell Schleicher. More specifically, this invention has to do with an improvement in the sensitized adsorfbent pigment coating member of the pressure-sensitized adsorbent pigment record material which serves as the print-receiving surface in conjunction with a printing fluid comprising normally colorless, color-reactable organic material that is converted to its colored form upon adsorptive contact with the sensitized pigment. This invention relates especially to an improved adsorbent pigment mixture.

A type of manifold printing record material which obviates the use of carbon paper is produced by coating sheet material with a multiplicity of pressure rupturable microscopic capsules of a printing fluid comprising an oily vehicle and at least one norm-ally colorless colorreactant organic material which turns to colored form upon contacting sheet material which has been properly sensitized. The manifold record material is assembled for manifold printing by stacking sheet material coated with encapsulated color-reactant organic material in faceto-face relationship with a sensitized coating on another sheet. Upon rupture of the capsules containing colorreactant material, as by printing pressure, the colorreactant organic material comes into adsorptive contact with the sensitized coating, producing a mark upon being transferred onto the sensitized coating. As in the production of other record forming material, the ultimate objective in formulating the constituents making up this type of record forming material is to obtain, at a reasonable cost, a very white printed sheet in which the print is registered accurately as uniform dark marks which clearly stand out from the white background.

One of the most practical forms of a manifold printing system of the type described above involves the use as the printing fluid of an encapsulated oily mixture of two particular color-reactant organic materials, namely crystal violet lactone (3,3 bis (p-dimethylamino-phenyl) 6-dirnethylaminophthalide) and benzoyl leuco methylene blue. The crystal violet lactone produces a :blue mark substantially immediately upon coming into adsorptive contact with a properly sensitized sheet. This mark, however, is evanescent in nature and the benzoyl leuco methylene blue forms a substantially permanent blue mark before the initially vformed mark fades. Therefore, a dark blue mark is present at all times after printing pressure is applied to the coating.

The print receiving sheet is sensitized by having finely divided solid adsorbent particles uniformly present on a surface. The adsorbent solid is a clay-like material which is acid relative to the organic printing fluid. Color conversion of the color-reactant organic printing fluid materials results from an electron donor-acceptor solid surface chemical reaction between the printing flui-d'and the sensitized adsorbent particles.

The clay that is commercially used in forming the sensitized print-receiving sheet when printing with the mixture of crystal violet lactone and benzoyl leuco methylene blue is a calcined grade of attapulgite clay. This particular type of clay is mixed with about 10% by weight of finely divided precipitated silica pigment. The silica is used to enhance the intensity of the initially formed mark since attapulgite clay used alone leaves something to be desired in this respect. This combination of pigment materials results in a coated receiving sheet which is exceptionally sensitive to a normally colorless mixture of crystal violet lactone and the leuco form of methylene blue and therefore acquires both a temporary and permanent dark blue color upon adsorptivecontact therewith.

To produce a sensitized sheet with attapulgite clay and silica, the pigment mixture is made up into a coating color containing water and a water-dispersible .adhesive to bind the pigment particles to the sheet. -In practice, the coating color is usually applied on-machine to the wire side of a sheet of raw stock. As in the case of other on-machine coating operations, it is considered highly desirable to apply the coating color at the highest possible pigment solids level consistent with the provision of a coating color of suitable viscosity. In this manner the load is reduced on the driers to which the freshly coated sheet is passed. This in turn permits operating at higher machine speeds and results in improved production rates.

Calcined attapulgite clay-silica pigment mixtures tend to body aqueous liquids to a greater extent than equivalent amounts of kaolin clay, a material which is widely used in making high grade coated stock. This is true of rnixtures of these pigments even when as little as 10% c01- loidal silica is used with the calcined clay. The presence of the colloidal silica is chiefly responsible since this material forms a thick gel-like system upon being agitated in water. '(W hile raw attapulgite clay behaves in a similar manner, the calcination to which the attapulgite clay has previously been subjected reduces materially the viscosity of aqueous suspensions of the clay per se.) Because of the presence of the colloidal silica, the permissible pigment solid level in coating colors made up with mixtures of calcined attapulgite clay and colloidal silica is less than the pigment solids level which can be used in making up coating colors with kaolin clay. Thus, for example, in a typical machine coating operation where viscosities (Brookfie'ld at '20 r.p.m.) of 2000-3000 cp. are about the maximum permissible, the highest pigment solids level which can be maintained with the calcined attapulgite clay-colloidal silica mixture of the prior art is within the range of about 30-35%, as compared with kaolin colors which can be used at solids content .as high as As a result, paper-forming and coating machines producing paper sensitized with a mixture of attapulgite clay and colloidal silica must be operated at a considerably lower speed than can be used with kaolin clay coating colors. Consequently, the possible rates of production of the sensitized paper falls very short of production rates obtainable in producing kaolin coated stock.

While it might therefore appear to be a logical expedient to use kaolin clay as the sole pigment or as an adjunct to calcined attapulgite clay in making a sensitized coating for manifold record material when using crystal violet lactone and the *leuco form of methylene blue as the printing fluid, this is not a satisfactory alternative. Kaolin clay, although it is an acid clay, is relatively insensitive to both crystal violet lactone and to the leuc form of methylene blue. As a result, only a very weak blue mark is obtained upon transfer of either of these materials to a sheet coated with kaolin clay. The mark is considered too weak for practical usage and does not compare favorably with the intensity of the mark obtained with attapulgite clay-colloidal silica mixtures. The same is also true of calcined kaolin clay whose sensitivity towards the dye mixture does not differ significantly from that of the uncalcined kaolin clay.

Accordingly, a principal object of the invention is the provision of a sensitized pigment mixture which produces a less viscous suspension in an aqueous adhesive vehicle than an attapulgite clay-silica mixture of the prior art at the same pigment solids level so that coating compositions made up with the improved pigment mixture may be applied at higher pigment solids levels, thereby permitting higher machine speeds in the coating operation.

Another object of this invention is the provision of an improved coating color composition for producing a sensitized coating on the receiving sheet of transfer printing material.

Further objects and advantages will be apparent from a description of this invention which follows.

This invention is the result of my discovery that the colloidal silica heretofore mixed with calcined attapulgite clay adapted for use in producing sensitized sheet material for transfer printing with benzoyl leuco methylene blue and crystal violet lactone can be replaced with multiple :benefits by kaolin clay which, prior to use, has been calcined and then subjected to controlled hydrothermal treatment, as described hereafter.

Stated briefly, the improved adsorbent pigment mixture of this invention consists of a major proportion by weight of calcined attapulgite clay with a minor weight proportion of an aluminum silicate having a BET. surface area of at least 120 sq. m./.gm., said silicate having been obtained by the following steps: (1) calcining kaolinite (a crystalline clay mineral of the approximate formula Al O .2SiO .2H O) at a temperature and for a time sufficient to remove substantially all the water of crystallization there-from, thereby forming a material usually referred to as metakaolin, this material being an amorphous material of the formula Al O .2SiO (2) subjecting the metakaolin to hydrothermal treatment under superatmospheric pressure .for a time preselected to restore most, but not all, of the theoretical water of crystallization t-o metakaolin, this resulting in an amorphous, high surface area, hydrous aluminum silicate of the approximate formula Al O .2SiO .(l.41.7)H O.

Water of crystallization is calculated as follows:

L.O.I. in the equation represents loss on ignition which is determined by heating the clay to constant weight at 1000 C. RM. represents free moisture which is determined by heating the clay to constant weight at 105 C. For convenience sake, the water of composition of the partially rehydrated metakaolin product will be referred to hereafter as water of crystallization although this product is amorphous or partially crystalline. The term amorphous is used herein in its usual sense and refers to the state of a material which is apparently noncrystalline in that it does not diifract X-rays.

The improved pigment mixture can be made up into Percent water of crystallization: X 100 coating colors containing from to total pigment solids without increasing the viscosity (B-rookfield at 20 r.p.m.) above the 2000-3000 cp. level. These improved coating colors contain about 10% more pigment solids than coating colors made up with the attapulgite-silica mixture of the prior art. This result is accomplished without sacrifice in the intensity of the mark obtained by printing the coated sheet with an encapsulated mixture of .benzoyl leuco methylene blue and crystal violet lactone. Sheet material coated with a coating color containing the improved sensitized pigment mixture is normally somewhat brighter than sheet material coated with a 90/10 mixture of attapulgite clay and silica.

The weight ratio of calcined attapulgite clay to high surface area partially rehydrated metakaolin pigments I employ is within the range of about 60 to 90 parts by weight of calcined attapulgite clay to about 40 to 10 parts by Weight of high surface area partially rehydrated metakaolin pigment. A preferred range of proportions is from to parts of calcined attapulgite to 25 to 15 parts of the rehydrated high surface area metakaolin. Proportions of pigments within the preferred range lead to the formation of coated sheets capable of registering printed impressions of optimum immediate and permanent intensity.

PREPARATION OF ATTAPULGITE CLAY PIGMENT The attapulgite clay used in forming the improved sensitized pigment mixture is a thermally activated grade. This form of the clay does not possess the colloidal properties of the raw clay. The clay is thermally activated by calcination at a temperature within the range of about 350 C. to about 600 C. for a time sufficient to reduce the V.M. of the clay to an amount within the range of about 8% to about 12%. Upon standing the calcined clay picks up moisture which results in an increase in the V.M. substantially above this level. The term volatile matter or V.M. as used herein refers to the weight percentage of the clay eliminated by heating the clay to essentially constant weight at 1000 C. The calcined atta-pulgite clay is cooled and ground to about minus 40 microns, as by fluid energy grinding. Good results are obtained by grinding to produce a material which is 50% by weight minus about 5 microns (equivalent spherical diameter).

PRODUCTION OF REHYDRATED METAKAOLIN PIGMENT (a) Preparation of metakaolin Kaolin clay (a clay consisting for the most part of the mineral kaolinite) is refined to the extent that grit (particles coarser than 44 microns) and undispersible agglomerates are removed. Coarse or fine fractions of clay may also be employed, if desired. Clays which have received other preliminary treatment, such as deironing or other beneficiation, may be used provided such treatment does not entail appreciable removal of alumina or silica or water from the clay. The clay is pulverized to render it all finer than about 325 mesh.

The crushed clay is initially calcined to eliminate substantially completely the water of crystallization, thereby converting the kaolin to metakaolin. The water of crystallization of the calcined product should not be more than about 2%, and is preferably less than 1%, to ob tain the maximum benefit of the subsequent hydrothermal treatment. In practice difficulty may be experienced in eliminating completely water of crystallization, and a water of crystallization of about 0.2% to 0.5% by weight in the metakaolin may be as low as can be practically attained. Calcination is carried out in air or steam, at atmospheric pressure or under vacuum, if desired. Ca1- cination temperature is critical only to the extent that the temperature must be high enough to effect complete conversion of the hydrous clay to metakaolin and yet be below that at which the characteristic kaolin exotherm occurs (940-980 C.). Calcination periods will usually fall within the limits of about /2 hour to 20 hours or more at temperatures of from about 450 C. to about 900 C. Calcination at temperatures below about 450 C. does not result in adequate loss of water of crystallization from the clay, even if calcination time is prolonged. When the clay is calcined at about 900 C. for a time sufficient to permit the kaolin exotherm to take place a profound change in the morphology of the calcined product occurs and pure metakaolin is not produced. Instead, a very dense material, believed by some authorities to be incipient mullite, is produced and this material is not amendable to the hydrothermal treatment hereafter set forth. The kaolin structure is substantially destroyed by the calcination as is evidenced by the absence of characteristic kaolin lines in the X-ray diffraction pattern of the calcined product.

(b) Hydrothermal treatment of metakaolin The metakaolin is cooled prior to hydrothermal treatment, since it has been found that subjecting the hot metakaolin to hydrothermal treatment so as to restore the controlled amount of water of crystallization thereto does not result in a product which has the desired high surface area as does the material produced when the metakaolin is cooled. Cooling is conducted in air or inert atmosphere until the metakaolin reaches ambient temperature or somewhat higher, but below about 125 C.

An aqueous slip of metakaolin is then prepared. The solids content of the slip may vary widely and good results have been realized operating with slips as dilute as solids (based on the composition weight) or as concentrated as 50% solids. More dilute slips may be used although for practical reasons slips less concentrated than 10% are not recommended. Apparatus and procedures for preparing clay slips are well-known to those skilled in the art.

The clay, in the form of an aqueous slip or paste, is subjected to hydrothermal treatment with saturated high pressure steam under conditions of time selected to restore water of crystallization to the dehydrated aluminum silicate in the amount within the limits of 10% to 12%, which is less than the theoretical water of crystallization of naturally occurring kaolin clay (13.9%). If desired, the slip may be formed in situ in the bomb when the calcined material is contacted with steam. Any suitable pressurized equipment provided with means for introducing and controlling pressurized steam may be employed. The hydrothermal treatment is carried out by directly contacting the metakaolin slip with saturated steam at a temperature up to but not including the critcal temperature of water. Since rehydration will be appreciably more rapid operating with saturated steam at relatively high pressure, the preferred hydrothermal treat ment is conducted with saturated steam at or above 800 p.s.i.g. For example, the desired degree of rehydration will be accomplished operating under the following approximate operating conditions using steam at saturation temperature: 300 p.s.i.g., for 60 hours; 400 p.s.i.g., for 28 hours; 500 p.s.i.g., for 8 hours; 800 p.s.i.g., for 2% hours; 1000 p.s.i.g. for 1 hour; 1200 p.s.i.g. for 1 /2 hours; 1400 p.s.i.g. for 30 minutes; and 1600 p.s.i.g. for 0 minutes. Time conditions refer to time after the reaction vessel reaches the indicated saturated steam pressure.

Rehydration may also be carried out on pressed cakes of metakaolin and such pressed cakes may be prepared by calcining mechanically compressed kaolin clay or by mechanically compressing finely divided metakaolin, preferably the former. However, it will be noted that clay which has been pressed (i.e., pelleted) before or after calcination does not necessarily respond to hydrothermal treatment as does pulverized clay and the desired high surface area product is obtained from pressed clay with high pressure saturated steam only when the density of the pressed product is between about 1.1 and 1.5 grams per cubic centimeter and hydrothermal conditions preselected to restore about 8.5% to about 12% water of crystallization to the dehydrated material.

The product obtained by hydrothermally treating metakaolin, under conditions described above, results in a high surface area hydrous aluminum silicate having a surface area within the range of about to 300 square meters per gram, sometimes more. These surface area values are considerably higher than those of either raw kaolin clay or metakaolin (which normally have surface areas of only 5 to 15 square meters per gram). Surface area values referred to in the specification and claims are so-called B.E.T. values, determined by a nitrogen adsorption method described by S. Brunauer, P. H. Emmett and E. Teller in their article entitled, Adsorption of Gases in Multi-Molecular Layers, on page 309 of Journal of the American Chemical Society, vol. 60, February 1938, using the molecular size data of H. K. Livingston presented in his article entitled, Cross-Sectional Areas of Molecules Adsorbed on Solid Surfaces, on page 569, Journal of the American Chemical Society, vol. 66, April 1944.

The surface area of the hydrous aluminum silicate obtained by hydrothermal treatment of metakaolin has been found to be independent of the temperature at which kaolinite was dehydrated to form metakaolin and the surface area is also independent of steam pressure and reaction time employed in the hydrothermal treatment since substantially the same product can be obtained by hydrothermal treatment at different saturated steam pressures. However, the surface area is apparently related to the amount of chemically combined water introduced into the metakaolin during hydrothermal treatment and to the amount of crystal structure obtained as measured by the intensity of the 7.2 A. d spacing on the X-ray diffraction pattern. Kaolin clay has an intense 7.2 A. d spacing on its X-ray diffraction pattern indicating a well-crystallized structure. Some samples of the high surface area partially rehydrated metakaolin may have a very weak 7.2 A. d spacing indicating the presence of kaolinite as a minor impurity. Other samples, especially those having an exceptionally high surface area, exhibit no 7.2 A. d spacing.

Reference is made to the inventors copending application Serial No. 213,039, filed July 27, 1962, which is a continuation-in-part of Serial No. 852,168, filed Novem ber 12, 1959, and abandoned August 3, 1962, for illustrative examples of the rehydration of kaolin clay to produce an amorphous high surface area partially rehydrated metakaolin.

The hydrothermally treated slip can be used directly in coating after adjusting the water content of the slip to a suitable level. Activated attapulgite clay pigment can then be incorporated into the slip. The high surface area rehydrated metakaolin pigment can also be supplied as a bone dry material suitably milled. It is also within the scope of this invention to use partially rehydrated metakaolin which has been calcined to a water of crystallization as low as about 2% at a temperature up to about 750 C. since the calcination does not impair the sensitivity of the pigment. The BET. surface area of the partially rehydrated metakaolin calcined at temperatures up to about 750 C. is substantially the same as the partially rehydrated metakaolin from which it is obtained.

PRODUCTION OF SENSITIZED COATED PAPER WITH PIGMENT MIXTURE The high surface area partially rehydrated metakaolin is mixed with heat activated attapulgite clay and the mixture dispersed in water using a small quantity pigment dispersant. A preferred dispersant is a mixture of a molecularly dehydrated phosphate with sodium silicate, such as the sodium silicate having a SiO :Na O mol ratio of about 3.2 to 1. The total quantity of dispersant employed is typically of the order of about 34% of the combined pigment weight. To the pigment dispersion is added a suitable adhesive or mixture of adhesives. The ratio of total pigment to adhesive solids is usually within the range of about 100 parts pigment to about to parts adhesive solids and varies prinicipally with the nature of the adhesive employed. The adhesive usually used in making kaolin coating colors may be used, e.g., synthetic latexes such as styrene-butadiene latex, starch adhesives such as enzyme-converted starch, oxidized starch, polyvinyl alcohol, casein or various mixtures thereof. The water content of the coating color is controlled to obtain a coating color having as high a pigments solids content as can be obtained without increasing the viscosity to a level at which the coating equipment can no longer handle and apply the coating. As mentioned, pigment solids contents of to are representative. In some cases coating colors containing pigment solids as high as can be produced without resulting in excessive viscosity.

The resultant coating colors are especially adapted for coating on-machine where normally they are applied to the wire side of a sheet of raw stock in amount such as to provide a uniform coat about 0.0005 inch thick. In making up manifold record material on-machine, an emulsion coating containing a mixture of crystal violet lactone and benzoyl leuco methylene blue is applied to the felt side of raw stock simultaneously with the application of a coating color containing the improved adsorbent pigment mixture of this invention to the wire side of the stock. In assembling the resultant finished coated sheets for manifold printing, a plurality of sheets are stacked in a manner such that the pigment coated surface of one sheet is in face-to-face relationship with a coating of rupturable encapsulated printing fluid on another sheet.

In U.S. 2,730,456 to Barrett K. Green and Lowell Schleicher, there is described a suitable method for producing a coating of a multiplicity of microscopic oil-containing encapsulated printing fluid. However, means for forming a coating of microscopic rupturable capsules containing color reactant other than the means described in said patent may be used in producing the transfer coating adapted for use with the coating of sensitized clay-like pigment of this invention since the sensitivity of the pigment is generally independent of the particular composition of the capsule shell. A typical composition of encapsulated printing fluid comprises about equal weight proportion of crystal violet lactone and benzoyl leuco methylene blue dissolved in trichlorodiphenyl or other water immiscible oil.

Also in accordance with this invention, the sensitized clay coating may be applied as a layer over a previously formed coating of encapsulated organic color-reactant materials or the latter coating may be applied directly over a layer of the pigment coating.

The following example illustrates the preparation of an adsorbent pigment mixture of this invention and the production of sensitized paper therewith.

(a) A sensitized adsorbent aluminum silicate was produced from kaolin clay as follows: The starting clay was a water-washed, degritted unfractionated kaolin clay from a mine near McIntyre, Georgia. The clay was composed primarily of well-crystallized kaolinite having an average equivalent spherical diameter of about 0.8 micron. The kaolin clay was pulverized in a high speed hammer mill and calcined in a preheated mutile furnace at 700 C. for 4 hours to produce metakaolin. The metakaolin was cooled to room temperature, pulverized and made into a 10% solids aqueous slip. The aqueous slip was placed in a stainless steel autoclave and subjected to the action of saturated steam at 1000 p.s.i.g. for one hour.

The slip was air dried at about 105 C. and the rehydrated metakaolin pulverized in a high speed hammer mill to an average particle size of about 5 microns (equivalent spherical diameter).

The surface area and Water of crystallization of the starting clay, intermediate products and calcined why u drated metakaolin products are given below to demonstrate the elfect of calcination or calcination and hydrothermal treatment upon the starting clay.

TABLE I.PROPERTIES OF HEAT AND/OR HYDRO- THERMALLY TREATED ALUMINUM SILICATES G.E. Water of B.E.T. pH of5% Block Crystal- Surface aqueous Brightlization, Area, suspenness, Percent mfl/gm. sion Percent (1) Kaolin clay 13. 71 11.3 5.5 (2) (1) Calcined 700 0J4 hr 78 0.86 12.1 5. 5 (3) (2) Rehydrated at 1,000

p.s.i./4 hr 82 11. 08 127. 0 4. 7

(b) coating colors were made up with each of the following siliceous materials as the pigment.

Pigment No. 1: Parts by wt.

Kaolin calc. at 700 C./4 hrs.; rehydrated 1000 P O :Na O ratio corresponding to the formula N 6P40l3) Sodium silicate (38% solids suspension, SiO :Na O

ratio of 3.221) 3.6 Enzyme-converted starch 6.0 Styrene-butadiene latex 9.7 Casein 0.9 Santomerse (aralkyl sulfonate wetting agent) 0.3

The procedure for preparing coating colors was as follows:

Six pounds of casein were soaked in Water at approximately 20% solids for 10 minutes prior to the addition of a pint of 28% ammonium hydroxide. The temperature of the casein suspension was raised to F. and maintained at this temperature for 10 minutes. The cooked casein was then added to a latex mixture prepared by dispersing 2 pounds of wetting agent in water and then adding pounds of 48% solids latex. Starch was mixed in water at about 25% solids and one gram of enzyme was added per pound of starch. The mixture was cooked for a total of 55 minutes, gradually raising the cooking temperature from F. to 210 F.

Quadrafos and sodium silicate (pigment dispersants) were dissolved in water and pigment was mixed in. The latex casein mixture, prepared in the manner described above, was then added to the pigment suspension following which the above'described enzyme converted starch mixture was added.

Using Pigment No. 2 (the calcined attapulgite claycolloidal silica mixture of the prior art), it was found that the maximum total pigment solids that could be used without increasing the Brookfield viscosity (20 rpm.) of the coating color above 2000 cp. was about 35%. At higher pigment solids loadings, the viscosity of the system fell outside a practical value. However, using Pigment No. 1, the 80/20 mixture of high surface area rehydrated metakaolin with calcined attapulgite, coating colors at about 45% solids had approximately the same Brookfield viscosity as the 35% solids coating color containing Syloid and attapulgite clay.

Sheets of raw paper stock were coated with Pigment No. 1 and with Pigment No. 2. In coating with the Pigment No. 1, the pigment mixture of this invention, an initial coating was applied at 40% solids at the rate of %-1 pound per ream (25" x 40"500). The sheet was dried to a moisture content in the range of 15% to 20% and the sheet was passed through two successive roll coaters, each of which applied 1 /2 to 1% pound per ream of coating at 45% solids. In coating with the attapulgite coating color, initial coating was at only 30% solids and the subsequent coating was at 35% solids.

It was found that the immediate and permanent dye sensitivity of the sheet coated in accordance with this invention with Pigment No. l was as good as that of the control (Pigment No. 2) in that the printed impression in each case was an intense dark blue color mark immediately after printing and after standing for several months.

I claim:

1. An improved sensitized color-reactable adsorbent pigment composition adapted for use in transfer printing with a mixture of benzoyl leuco methylene blue and crystal violet lactone comprising a mixture of:

a major weight proportion of heat activated attapulgite clay and a minor weight proportion of a white aluminum silicate having a BET. surface area of at least about 120 sq. m./gm.,

said aluminum silicate having been obtained by cal cining kaolin clay at a temperature and for a time to produce metakaolin, cooling said metakaolin to a temperature below about 125 C., and subjecting said metakaolin to hydrothermal treatment at superatmospheric pressure at a temperature and for a time selected to convert said metakaolin into an amorphous aluminum silicate of the approximate formula Al O .2SiO (1.4-1.7 H

2. The composition of claim 1 wherein said aluminum silicate is present in amount within the range of 10:40 parts by weight to 90:60 parts by weight of said attapulgite clay.

3. The composition of claim 2 wherein said aluminum silicate is present in amount within the range of 15:25 parts by weight to 85:75 parts by weight of said attapulgite clay.

4. A composition for applying to paper to provide thereon a coating sensitized to a mixture of benzoyl leuco methylene blue and crystal violet lactone which comprises water containing dispersed adsorbent pigment particles and an adhesive for said adsorbent pigment particles, the major Weight proportion of said adsorbent pigment particles being thermally activated attapulgite clay,

the remainder of said adsorbent pigment particles being a white aluminum silicate having a BET. surface area of at least about 120 sq. m./gm., said aluminum silicate having been obtained by calcining kaolin clay at a temperature and for a time to produce metakaolin, cooling said metakaolin to a temperature below about 125 C., and subjecting said metakaolin to hydrothermal treatment at superatmospheric pressure at a temperature and for a time selected to convert said metakaolin into an amorphous aluminum silicate of the approximate formula Al O .2SiO (1.4-1.7 H O), the concentration of said adsorbent pigment particles in the system being within the range of from about 40% to about 50% by weight, and the Brookfield viscosity of said composition not substantially exceeding about 3000 cp. at 20 rpm. 5. The composition of claim 4 wherein said aluminum silicate is present in amount within the range of :40 parts by weight to 90:60 parts by weight of said attapulgite clay.

6. The composition of claim 4 wherein said aluminum 30 silicate is present in amount within the range of :25 parts by weight to 85:75 parts by weight of said attapulgite clay.

References Cited by the Examiner UNITED STATES PATENTS 2,699,432 1/1955 Marra et al. 106-214 3,014,836 12/1961 Proctor 106-288 FOREIGN PATENTS 815,924 7/1959 Great Britain.

TOBIAS E. LEVOW, Primary Examiner. 

1. AN IMPROVED SENSITIZED COLOR-REACTABLE ADSORBENT PIGMENT COMPOSITION ADAPTED FOR USE IN TRANSFER PRINTING WITH A MIXTURE OF BENZOYL LEUCO METHYLENE BLUE AND CRYSTAL VIOLET LACTONE COMPRISING A MIXTURE OF: A MAJOR WEIGHT PROPORTIN OF HEAT ACTIVATED ATTAPULGITE CLAY AND A MINOR WEIGHT PROPORTION OF A WHITE ALUMINUM SILICATE HAVING A B.E.T. SURFACE AREA OF AT LEAST ABOUT 120 SQ. M./GM., SAID ALUMINUM SILICATE HAVING BEEN OBTAINED BY CALCINING KAOLIN CLAY AT A TEMPERATURE AND FOR A TIME TO PRODUCE METAKAOLIN, COOLING SAID METAKAOLIN TO A TEMPERATURE BELOW ABOUT 125*C., AND SUBJECTING SAID METAKAOLIN TO HYDROTHERMAL TREATMENT AT SUPERATMOSPHERIC PRESSURE AT A TEMPERATURE AND FOR A TIME SELECTED TO CONVERT SAID METAKAOLIN INTO AN AMORPHOUS ALUMINUM SILICATE OF THE APPROXIMATE FORMULA AL2O3$2SIO2 (1.4-1.7 H2O). 